The application of fiber-optic devices to various measuring circuits is known in the prior art. For instance fiber-optics have been extensively employed in Mach-Zehnder interferometers. In such devices one optical fiber is used as a standard and another is associated with an apparatus that experiences a physical dimension change in response to a phenomenon. That change induces a length change in the optical fiber which, in turn, causes a phase change in light in the fiber. When the altered phase is compared against the phase in the standard fiber, a measurement of the phenomenon which caused the physical change is obtained. Such interferometers are described in an article entitled "An Overview of Mach-Zehnder Interferometric Sensors", Watanabe et al., SPIE, Vol. 566, Fiber Optic and Laser Sensors, III, 1985, pp. 16-21.
A fiber-optic sensor for detecting magnetic fields is described in an article entitled "All Single Mode Fiber Magnetic Field Sensor", Cork et al., SPIE, Vol. 566, Fiber Optic and Laser Sensors, III, pp. 294-299. In that sensor, the fiber which serves as the phase standard is coiled around a piezo-electric cylinder that is in turn, employed as an active phase compensator to maintain the interferometer at its point of maximum sensitivity. The sensing fiber leg is juxtaposed to a Metglass sensing element which induces phase changes in the associated fiber. In such interferometric sensors, the circuitry required to detect and analyze the phase changes of the transmitted light beams are both expensive and complex.
A variety of fiber optic sensors have been applied to the sensing and measurement of various types of magnetic fields. For instance, in U.S. Pat. No. 4,516,021 to Taylor a birefringent optical fiber is employed in combination with a magnetostrictive block that induces strains in the fiber in response to an applied magnetic field. Any change in birefringence in the fiber is measured by directing the light exiting the fiber through a polarizer or prism and then detecting the change in intensity modulation in a photodetector.
In U.S. Pat. No. 4,603,296 to Koo et al. a magnetometer is described that uses interferometric principles to detect changes in a magnetic field. The fiber used as the sensor is associated with a magnetostrictive jacket, and thus has its length altered by alterations of the jacket in a magnetic field. A phase detector produces signals proportional to the resulting phase shift.
In U.S. Pat. No. 4,622,460 to Failes et al. a further fiber-optic magnetic sensor is disclosed which, as above, causes changes in the length of the fiber as a result of deformations of magnetic sensors. In each of the above cases, the fiber optic system is used to measure changes in a magnetic field, which changes induce strains in a measuring optical fiber to thereby enable measurements of the altered magnetic field.
Optical fibers have also been employed to measure current and/or voltage. In U.S. Pat. No. 4,547,729 to Adolfsson et al., an optical fiber system is employed to measure the voltage applied to a piezo-electric transducer. In specific, a mirror is connected to the piezo-electric transducer and, dependent upon the amount of voltage applied thereto, deflects the mirror and reflects either more or less light back onto a receiving fiber sensor. Thus, the system employs alterations in reflected light to achieve its measurements, notwithstanding the use of optical fibers.
In certain industrial environments, high voltages are present which must be accurately measured in order to assure proper operation of devices dependent thereupon. For instance, electron beam welding requires precise measurement of high voltages to produce acceptable welds. Unfortunately, in the environment of electron beam welders, extremely high fields are present which make impractical normal conductive type measuring circuits and devices. Similar environments exist in radar, sonar, and pulsed high voltage applications.
Accordingly, it is an object of this invention to provide an optical sensor particularly adapted to working in high field environments.
It is a further object of this invention to provide an optical sensor particularly adapted to measuring voltages in high noise/field environments while additionally providing for personnel safety via isolation of the management instruments.